This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The current project is designed to investigate one well documented gene-to-cognition relationship within a novel population. Specifically, blood samples will be collected from prior research subjects with Parkinson's disease, who have already undertaken behavioral and PET (Positron Emission Tomography)imaging examination. Patients'Catechol-O-Methyltransferase (COMT) genotype (Val (108/158 Met) will be determined and results compared to prior imaging and behavioral findings.